used with dimethylformamide (DMF), dimethylsulfoxide (DMSO), or gamma butyrolactone. [1b,3,4] The precursor film is then converted to the perovskite structure by annealing on a hot plate at 60-200 °C. The high temperature treatment however spoils the film properties by generating intrinsic defects, stoichiometric or compositional changes, rapid film degradation, uncontrollable perovskite precipitation, inhomogeneous perovskite crystallization at the perovskite/underlayer interface, and incomplete surface coverage with a random film texture. [5] To avoid high temperature annealing processes, solution-based methods have been developed. However, in those studies, the perovskite colloidal particles are synthesized in solution and then deposited on the underlayer film without elimination of annealing. [6][7][8] They are enabled by the addition of small molecules, use of an excess organic component, or treatment with hypophosphorous acid. Therefore, these solution reactions still require high temperature and thus cannot avoid unmanageable surface reactions resulting in nonstoichiometric dopants and phase segregation. [9] In order to lower the reaction temperature, acid-treated methods including acidcatalyzed techniques [10] and acid-base solutions [11] have been developed particularly for mixed [12,13] and single halides [14] in DMF. [15][16][17][18][19] The acid-catalyzed reactions are, in general, initiated by the formation of solvated PbI 4 2− anions that further react with CH 3 NH 3 + cations for CH 3 NH 3 PbI 3 (s) (MAPbI 3 ) Methylammonium lead iodide (MAPbI 3 ) perovskites are organic-inorganic semiconductors with long carrier diffusion lengths serving as the light-harvesting component in optoelectronics.Through a substitutional growth of MAPbI 3 catalyzed by polar protic alcohols, evidence is shown for their substrate-and annealing-free production and use of toxic solvents and high temperature is prevented. The resulting variable-sized crystals (≈100 nm-10 µm) are found to be tetragonally single-phased in alcohols and precipitated as powders that are metallic-lead-free. A comparatively low MAPbI 3 yield in toluene supports the role of alcohol polarity and the type of solvent (protic vs aprotic). The theoretical calculations suggest that overall Gibbs free energy in alcohols is lowered due to their catalytic impact. Based on this alcohol-catalyzed approach, MAPbI 3 is obtained, which is chemically stable in air up to ≈1.5 months and thermally stable (≤300 °C). This method is amendable to large-scale manufacturing and ultimately can lead to energy-efficient, low-cost, and stable devices.

Interfacial interactions between halides of the perovskite precursors and the oxygen groups of GO reduce GO, and determine perovskite yield.

Silver nanoparticle-modified graphene oxide (Ag/GO) was reliably prepared by using sodium borohydride (NaBH4) in the presence of citric acid capping agent via a simple wet chemistry method. This rapidly formed Ag/GO composite exhibited good dispersity in a solution containing hydrophilic polyacrylonitrile (PAN). Subsequent electrospinning of this precursor solution resulted in the successful formation of nanofibers without any notable defects. The Ag/GO-incorporated PAN nanofibers showed thinner fiber strands (544 ± 82 nm) compared to those of GO-PAN (688 ± 177 nm) and bare-PAN (656 ± 59 nm). Subsequent thermal treatment of nanofibers resulted in the preparation of thin membranes to possess the desired pore property and outstanding wettability. The Ag/GO-PAN nanofiber membrane also showed 30% higher water flux value (390 LMH) than that of bare-PAN (300 LMH) for possible microfiltration (MF) application. In addition, the resulting Ag/GO-PAN nanofiber membrane exhibited antibacterial activity against Escherichia coli (Gram-negative) and Staphylococcus aureus (Gram-positive). Furthermore, this composite membrane exhibited outstanding anti-fouling property compared to the GO-PAN nanofiber membrane in the wastewater treatment. Therefore, the simple modification strategy allows for the effective formation of Ag/GO composite as a filler that can be reliably incorporated into polymer nanofiber membranes to possess improved overall properties for wastewater treatment applications.

No abstract

Since carbon tetrahalides CX 4 (X = Cl/Br) are adsorbed on carbon nanotubes and graphene sheets, we have studied the structures, adsorption energies, and electronic properties of CX 4 adsorbed on benzene, coronene, and graphene using dispersion corrected density functional theory (DFT) with hybrid functionals. As compared with the benzene−CX 4 complexes (with binding energy of ∼14/15 kJ/mol) where electrostatic energy is significant due to the halogen bonding effect, the graphene−CX 4 complexes show about three times the benzene−CX 4 binding energy (∼40/45 kJ/mol) where the dispersion interaction is overwhelming with insignificant electrostatic energy. Since the X atoms in CX 4 are slightly positively charged and the X atom's ends are particularly more positively charged due to the σ-hole effect, CX 4 behaves as an electron acceptor. This results in electron transfer from locally negatively charged C sites of benzene/coronene to CX 4 . In contrast, no electron transfer occurs from graphene to CX 4 because of the large work function of graphene and significant electron affinity of CX 4 and because homogeneously charge-neutral graphene has no locally charged sites. Nevertheless, due to the symmetry breaking upon adsorption, the CX 4adsorbed graphene shows a small band gap opening without p-doping. On the other hand, CF 4 behaves as an electron donor due to the negatively charged F atoms, which results in electron transfer from CF 4 to the locally negatively charged C sites of benzene/coronene. Again, no electron transfer occurs from CF 4 to graphene because of high ionization energy of CF 4 , and so the CF 4 -adsorbed graphene opens only a small band gap without n-doping.